The objective of this research is the isolation and molecular structure determination of bioactive constituents of marine organisms, particularly sponges, mollusks and tunicates. Freeze-dried organisms are extracted with water and with an organic solvent. Both extracts are assayed for cytotoxicity (KB cell line) and structural features (1H NMR). Those samples which show promising activity (MIC < 1 mug/mL) are purified by solvent partition and chromatography. The KB assay is used to guide the fractionation. Pure samples, as judged by HPLC, are subjected to spectral analysis (1H and 13C NMR, MS, UV, IR) in order to determine the molecular structure. MARINELIT and CAS ONLINE are used to determine whether the compound is new. All compounds, new and those described previously, are submitted to the National Cooperative Natural Products Drug Discovery Program for assay against solid tumors; to NCI for broad anti-tumor and anti-AIDS assays; and to Pharma Mar, S.A. for antiviral, antimicrobial, and immunomodulatory activities. For active samples which are slated for in vivo assay re-isolation and/or recollection may be necessary.